Answers
1

1) We are never told why Montgomery left London, except for a brief comment in Chapter Two, which declared he had "made a young ass of [himself]."

2) From the text:

"The creature’s face was turned for one brief instant out of the dimness of the stern towards this illumination, and I saw that the eyes that glanced at me shone with a pale-green light. I did not know then that a reddish luminosity,

at least, is not uncommon in human eyes. The thing came to me as stark inhumanity. That black figure with its eyes of fire struck down through all my adult thoughts and feelings, and for a moment the forgotten horrors of childhood."